1. Field of the Invention
The present invention relates to a signal level conversion circuit, and more particularly to a bidirectional conversion circuit capable of reducing the number of circuit elements without receiving restriction of utilized power supply voltages.
2. Description of the Related Art
Semiconductor integrated circuit (LSI) including a logic circuit or a sequence circuit formed of CMOS (Complementary Metal Oxide Semiconductor) transistors is generally provided with a signal conversion circuit to shift a signal level between different high potential power supplies. There are two types of the signal level conversion circuit which carries out the level conversion of the signal level. One is one way type in which the signal passes in one direction. Another is a bidirectional type in which the signal passes in both directions using two power sources. The two power-supply bidirectional type signal level conversion circuit is suitable for three or more electrical power systems.
In a Japanese laid open patent application No. 2007-228407, it is necessary to form a protection diode in a direction from an input/output terminal to a high potential power supply source in a signal level conversion circuit accepting three or more electrical power systems. When the protection diode is not formed in the direction from the input/output terminal to the high potential power supply source, there is a problem of receiving restriction of a level of the utilized power supply voltage (an input tolerant function is lost). Moreover, in this Japanese laid open patent application, since a bus switch is used as a level shift circuit, there is a problem that high speed correspondence is difficult.